Corrugated paperboard sheets may be formed into stacks by being stopped and then allowed to drop onto a descending elevator. Tines may be moved through the board line to temporarily support a newly forming stack while a fully formed stack is lowered further on the elevator and then ejected to a discharge conveyor. Apparatus for so forming such stacks is disclosed in U.S. Pat. No. 4,500,243 and U.S. Pat. No. 4,632,378. These are examples of so called die-cut stackers.
When making corrugated paperboard container blanks, printed and creased/slotted blanks may have two flaps folded over and glued together. These folded and glued blanks are then stacked for shipment or storage. This stacking is usually performed immediately after the folded and glued blanks leave a folder-gluer machine and while the glue has not properly dried or set. Stacking of these glued blanks is usually performed on so called counter ejectors.
As stacking speeds increase, it becomes more important to ensure in both die-cut stackers and counter ejectors that the leading edge of a following sheet does not get underneath the trailing edge of the sheet in front during the stacking procedure.
Also, particularly with counter ejectors where the freshly glued flaps tend to unfold and come apart, it is desirable to control the top of a stack while being formed and when fully formed. This presents new problems as stacking speeds increase, particularly with corrugated paperboard sheets which can readily be damaged by crushing.